The invention relates to extreme pressure additives for lubricating oils. More particularly, the invention relates to the finding that the extreme pressure properties of a lubricant are greatly improved by the addition of a specific mixture of phosphates, said phosphates comprising: (a) substituted dithiophosphates and (b) mono and disubstituted sulfur-free phosphates wherein the composition has been neutralized by reaction with a hydrocarbyl amine.
Lubricants containing dithiophosphates per se, monothiophosphates per se and mono and disubstituted phosphates per se are well known in the art. For example, U.S. Pat. No. 4,431,552, which discloses a borate-containing lubricant composition also containing a mixture of phosphates, monothiophosphates and dithiophosphates in a critical ratio. In the present invention it has been found that monothiophosphates adversely effect the extreme pressure properties of the lubricant.
It is an object of the present invention to provide a lubricant having improved extreme pressure properties. The improved properties are obtained through the combination of specific phosphates which have been neutralized by a hydrocarbyl amine.